Electric discharge lamp having improved mercury-vapor control assembly

ABSTRACT

The mercury-vapor pressure within a fluorescent lamp is controlled by an amalgam-forming metal that is enclosed in a foraminous container supported at a selected location within the lamp envelope. The container is fabricated from two strips of wire mesh that are arranged in overlying enclosing relationship with a strip of amalgam-forming metal to form an assembly that is secured to one of the lamp stems. Leakage of the amalgam-forming metal and amalgam when in a fluid state is prevented by providing a border of overlapped wire mesh that is devoid of metal and extends around the periphery of the assembly. Alternatively, the border extends along the sides of the assembly and the ends of the assembly are rendered leakproof by a coating of a material that repels the amalgam or amalgam-forming metal. A method and apparatus for making continuous border-type assemblies on a mass production basis are also disclosed.

United States Patent Inventor George S. Evans Caldwell, NJ.

Appl. No. 32,924

Filed Apr. 29,1970

Patented Oct. 19, 1971 Assignee Westinghouse Electric Corporation Pittsburgh, Pa. Continuation of application Ser. No. 524,907, Feb. 3, 1966. i

ELECTRIC DISCHARGE LAMP HAVING IMPROVED MERCURY-VAPOR CONTROL ASSEMBLY 8 Claims, 7 Drawing Figs.

US. Cl 313/174,

29/200, 29/505, 313/109, 313/178, 417/48 Int. Cl ll0lj61/24 Field of Search 313/174,

[56] References Cited UNITED STATES PATENTS 3,007,071 10/1961 Lompe et al 313/109 X Primary Examiner-Raymond F. Hossfeld Attorneys-A. T. Stratton, W. D. Palmer and D. S. Buleza ABSTRACT: The mercury-vapor pressure within a fluorescent lamp is controlled by an amalgam-forming metal that is enclosed in a foraminous container supported at a selected location within the lamp envelope. The container is fabricated from two strips of wire mesh that are arranged in overlying enclosing relationship with a strip of amalgam-forming metal to form an assembly that is secured to one of the lamp stems. Leakage of the amalgam-forming metal and amalgam when in a fluid state is prevented by providing a border of overlapped wire mesh that is devoid of metal and extends around the periphery of the assembly. Alternatively, the border extends along the sides of the assembly and the ends of the assembly are rendered leakproof by a coating ofa material that repels the amalgam or amalgam-forming metal. A method and apparatus for making continuous border-type assemblies on a mass production basis are also disclosed.

PATENIEUOBHQIQH 14 5 ELECTRIC DISCHARGE LAMP HAVING IMPROVED MERCURY-VAPOR CONTROL ASSEMBLY CROSS-REFERENCES TO RELATED APPLICATIONS The present application is a continuation of application Ser. No. 524,907 filed Feb. 3, 1966, and discloses and claims an improvement over the subject matter of copending application Ser. No. 381,503 entitled MERCURY VAPOR DISCHARGE LAMP AND PRESSURE REGULATING MEANS THEREFOR" of George S. Evans, the present inventor, which application was filed July 9, 1964, and is assigned to the same assignee as the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to electric discharge devices and has particular reference to a fluorescent lamp having an improved assembly for controlling the mercury-vapor pressure within the lamp during operation.

2. Description of the Prior Art Mercury-vapor discharge lamps having an amalgam which controls the mercury-vapor pressure within the lamp during operation are, per se, well known in the art. A lamp of this type is disclosed in US Pat. No. 3,007,071 issued Oct. 31, 1961 to A. Lompe et al.

In the aforementioned copending Evans application Ser. No. 381,503 the mercury-vapor pressure within a fluorescent lamp is controlled by an amalgam of a selected parent metal and mercury that is held at a predetermined location on the lamp stem by a collar which is fabricated from wire cloth or mesh. Since the vapor pressure above the amalgam is less than that above liquid mercury at the same temperature, the use of such an amalgam as the vapor control means permits the lamp to be operated at optimum efficiency over a much wider range of ambient temperatures. This is a distinct advantage in outdoor lighting applications and in applications where the lamp is operated in a totally enclosed fixture.

In accordance with the preferred method of fabricating such collar assemblies disclosed in the aforesaid copending Evans application, a mercury-amalgamative metal, such as indium, is sandwiched between two pieces of suitable foraminous material, such as nickel wire mesh, by feeding continuous strips of these materials between a pair of rollers. The resulting continuous lamination is then cut into sections of the required length and formed into an annular collar that is attached to one of the lamp stems. The strips of wire mesh are wider than the indium strip and the latter is centrally located between the wire mesh members, thus leaving a border along each side of the resulting lamination that is free of indium. These borders act as buffer zones or barriers which prevent the molten indium from migrating to and leaking out of the sides of the collar during the sealing-in and other phases of lamp fabrication that heat the stem to a temperature above the melting point of the indium. However, experimental runs in the factory revealed that drops of molten indium would frequently fall off the cut ends of the collar where the indium was exposed. Excessive amounts of such loose indium in the finished lamp would, of course, alter the mercury-vapor pressure during operation and could adversely affect both the performance and quality of the lamps.

OBJECTS AND SUMMARY OF THE INVENTION It is accordingly the general object of the present invention to provide an electric discharge device, such as a fluorescent lamp or the like, that has an improved mercury-vapor control assembly which obviates the foregoing and other problems associated with the use of an amalgam as the pressure-regulating means in such devices.

Another and more specific object is the provision of a fluorescent lamp which has a mercury-vapor control assembly which will retain the amalgam-forming metal, even when the latter is in a fluid state and the lamp in which the assembly is sealed is being handled and subjected to the various factory operations required to complete, test and pack such lamps.

The foregoing objects, and other advantages which will become apparent as the description proceeds, are achieved in accordance with one embodiment of the present invention by coating the cut ends of the laminated collar assembly with a material which repels the molten amalgamative metal, or is less susceptible to wetting by such metal than the strips of wire mesh. This coating thus serves as a barrier which, in conjunction with the borders along the sides of the assembly that are free of amalgam-forming metal, effectively restricts the movement of the metal and preventsit from leaking out of the assembly, even when the metal is in a fluid state. In the case ofa collar fabricated from nickel wire mesh and indium, the aforesaid end barrier preferably consists of a coating of indium oxide and nickel oxide on the exposed portions of the respective metals that extends inwardly a predetermined distance from each end of the collar.

In another embodiment the collar is rendered leak-proof" by providing an indium-free border at each end of the assembly as well as along its side edges. The sandwiched strip of indium, or other suitable amalgamative metal, is thus completely encircled by a fence of overlapped wire mesh that is free of such metal and thus prevents drops of molten metal from collecting at and dropping off the edges of the collar.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the invention will be obtained by referring to the accompanying drawing, in which:

FIG. 1 is an elevational fragmentary view of a fluorescent lamp embodying the present invention, a portion of the bulb being removed for convenience of illustration;

FIG. 2 is an enlarged perspective view of a lamp mount and attached mercury-vapor pressure control collar of the present invention;

FIG. 3 is an enlarged fragmentary plan view of one form of laminated assembly from which the aforesaid collar is formed, portions of the various layers being removed and peeled back to illustrate the construction;

FIG. 4 is a similar view of another embodiment wherein the assembly is provided with border that is devoid of amalgamforming metal and extends completely around the periphery of the assembly;

FIG. 5 is a side view illustrating the first stage in fabricating assemblies of the type shown in FIG. 4 utilizing a preferred form of roller which simultaneously compresses and cuts preselected portions of the strip of amalgam-forming metal;

FIG. 6 is a fragmentary side view of the partly fabricated lamination illustrating an optional step in the manufacturing process; and

FIG. 7 is a view similar to FIG. 5 illustrating the final pressing operation according to the process.

While the present invention can be used with advantage in various types of gaseous discharge devices that require a vapor control component, it is particularly adapted for use in fluorescent lamps and has accordingly been so illustrated and will be so described.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawing in detail, in FIG. 1 there is shown a fluorescent lamp 10 comprising a vitreous tubular envelope 12 that has the customary coating 14 of suitable ultraviolet-responsive phosphor on its inner surface and the usual electrode mounts l6 sealed into each. of its ends. Each of the mounts supports a cathode 18 that is connected by lead wires 19 and 20 to the terminals of a suitable base member 22 attached to each end of the envelope. One of the mounts 16 is provided with a tubulation that is tipped off in a usual manner after the lamp has been evacuated, dosed with mercury and filled with a suitable inert starting gas such as argon, neon or a mixture thereof. The other mount (located at the left end of the lamp 10 as viewed in FIG. 1) is fitted with a mercury-vapor pressure control assembly 28.

As is illustrated more clearly in FIG. 2, the aforesaid mount 16 consists of the usual flared vitreous stem 24 and lead wires 19 and 20 which support the cathode l8 and are sealed through a press formed on one end of the stem tube. A pair of enlarged metal anode 25, 26 are also disposed on opposite sides of the cathode l8 and are held in this position by the inner ends of the respective lead wires. The control assembly 28 consists of a strip of suitable amalgamative material, such as indium, that is sandwiched between two strips of foraminous metal, such as nickel wire mesh. The resulting lamination is bent into a collar that is slipped over the stem tube 24 and held in encircling relationship therewith by a resilient wire clamp 30. A mount of this type and the manner in which the laminated collar assembly 28 controls the mercury vapor pressure within the lamp during operation is described in detail in the aforesaid copending application Ser. No. 381,503 of the present inventor.

The present application is directed to the problem of retaining the amalgam-forming metal on the control assembly and within the cellular structure of the wire mesh members during the sealing-in and subsequent phases of lamp manufacture when the metal is in a liquid state. Improved control assemblies which overcome this problem, and a method and apparatus for manufacturing them will now be described.

In FIG. 3 there is shown one form of laminated assembly 28 for overcoming the leakage problem associated with the use of relatively soft amalgam-forming metals such as indium. As illustrated, the assembly (prior to being bent into collar form) consists of an elongated rectangular strip of indium 32 that is sandwiched and centrally located between two rectangular strips 34 and 36 of suitable foraminous material such as nickel wire mesh. Since indium is a relatively soft metal at room temperature, the pressure applied to the overlying strips of wire mesh in forming the lamination partly embeds them in the indium. This welds or binds the various strips together into an integral assembly that can be handled and bent without coming apart.

As will be noted, the wire mesh strips 34 and 36 are wider than the indium strip 32. There is, accordingly, a margin or border B of overlapped wire mesh that extends along each side of the assembly and is devoid of indium. These indium-free borders act as barriers which prevent the leakage of molten indium from the sides of the collar, even though the wire mesh strips are fabricated from nickel or other suitable material that is wet by the amalgam-forming metal in accordance with the teachings of the aforesaid copending application.

The leakage of molten indium from the cut ends of the laminated assembly 28 is prevented in accordance with this embodiment by coating the ends of the indium and wire mesh strips with a substancethat repels indium, or which is less susceptible to wetting by indium than the wire mesh members. In the particular case of indium and nickel, the exposed end surfaces of the indium and nickel wire mesh strips are coated with a layer of indium oxide and nickel oxide, respectively. This coating extends inwardly a predetermined distance from each of the cut ends of the assembly 28 and completely across the lamination, thereby providing a region E at each end that merges with the indium-free border B, as shown in FIG. 3.

Tests have shown that neither indium nor indium-mercury amalgam will migrate over oxidized nickel and that they are also effectively blocked by oxidized indium. The invention, however, is not limited to these specific materials and retention of the molten amalgam-forming metal during lamp manufacture can also be achieved by oxidizing the end portions of the lamination regardless of the materials from which it is made. Copper oxide for example, exhibits the same properties in this regard as nickel oxide. Tests have shown that in the case of a 96 inch, 1.5 ampere fluorescent lamp having an envelope l-l inches in diameter (T12), the indium-free borders B and oxidized zone E should both be at least one-sixteenth of an inch wide.

The ends of the assembly 28 can be oxidized by heating them with an intense flame, while the body portion of the as- ALTERNATIVE EMBODIMENT (FIG. 4)

In FIG. 4 there is illustrated another embodiment wherein the desired retention of the amalgam-forming metal is achieved by means of a border B that extends completely around the periphery of the laminated assembly 280 and is devoid of such metal. In this embodiment, the strip 32a of indium is not only narrower but shorter than the wire mesh strips 34a and 36a between which it is sandwiched. The relative dimensions of the strips are such that the edges of the centrally located indium strip 32a is spaced inwardly from the edges of the aligned overlying wire mesh strips 34a and 360 at least one-sixteenth of an inch. The indium, or other amalgam-forming metal that is used, is thus confined within a border B that consists of contiguous overlapped portions of the wire mesh strips.

MANUFACTURING METHOD AND APPARATUS (FIGS. 5-7) While an assembly of the type shown in FIG. 4 can be manufactured by stacking individually cut pieces of wire mesh and amalgam-forming metal in the proper relationship and then compressing them to force the metal into the mesh openings, this would be a time-consuming and costly operation since a soft metal such as indium is very difficult to cut and handle and the severed edges of the mesh members inherently tend to become entangled. A continuous method of fabrication would, of course, be more efficient and practical, especially in view of the fact that fluorescent lamps are manufactured on a mass production basis. Such a method and a preferred apparatus for practicing it are shown in FIGS. 5 and 7, and will now be described.

As shown in FIG. 5, the first step of this method comprises placing a continuous strip 32 of indium in overlying relationship with a continuous strip 340 of wire mesh and feeding the two strips between a pair of rollers 38 and 40 which rotate in opposite directions as indicated by the arrows and are so spaced that the wire mesh strip is pressed into and at least partly embedded in the indium strip. The roller 40 which contacts the indium strip 32' is provided with a pair of suitable cutting elements such as knives 41 and 42 that extend transversely across and project from the work face of the roller. The knives project beyond the work face of roller 40 a distance substantially equal to the thickness of the indium strip 32' and are spaced apart a distance equal to approximately twice the width of the indium-free border B desired at the cut ends of the completed assembly 280. The peripheral distance from the knife 41 around the work face of the roller 40 to the other knife 42 is equivalent to the length of the individual pieces 32a of iridium required for the collar assemblies 28a.

Thus, the rollers 38 and 40 concurrently press the first wire mesh strip 34a into the indium strip 32' and form a series of closely spaced transverse cuts 43 and 44 in the latter which divides it into alternately disposed long segments 32a and short segments 45, as shown in FIG. 5. A recess 46 is also provided in the work face of the roller 40 between the knives 41 and 42, thereby forming a relief cavity or pocket that extends across the roller face. Thus, only the longer segments 32a of indium are pressed against and bonded to the wire mesh strip 340, whereas the short segments 45 merely lie on top of the mesh, as indicated in FIG. 5.

The short segments 45 of indium are then removed from the wire mesh strip 34a by a jet of compressed air or suitable mechanical means (not shown). If desired, such removal can be achieved with the aid of gravity by inverting the lamination produced by the rollers 38 and 40 so that the indium segments 32a and 45 face downwardly.

Alternatively, the aforesaid lamination may be bent along an axis located between the pair of cuts 43 and 44 in the indium strip, as shown in FIG. 6, in a direction such that the short segments 45 of indium are bent into an arch and separated from the underlying mesh strip 34a. The protruding segments are then stripped from the mesh by a suitable tool.

The removal of the aforesaid short segments of indium provides a continuous ribbon or lamination, such as that shown in the left-hand portion of FIG. 7, which consists of bonded strip 34a of wire mesh and a plurality of indium segments 32a that are of uniform length and separated by a series of indium-free gaps G. This lamination is then aligned with a second strip 36a of wire mesh and the two components are fed through a second set of pressing rollers 48 and 50, as shown in FIG. 7. This completes the bonding operation and produces a continuous mesh indium-mesh lamination having a series of uniformly spaced transversely extending gaps G that are devoid of indium. This final lamination is then out along lines which bisect the aforementioned gaps, thereby producing a plurality of assemblies 280 of the type shown in FIG. 4.

Since indium is very soft, even at room temperature, it may stick to the roller 40 used in the first pressing operation. Hence, this roller (or at least its work face) is fabricated from a material, such as a suitable plastic, that is harder than and does not adhere to indium or indium-rich alloys at room temperature. An example of a suitable plastic is nylon.

It will be appreciated from the foregoing that the objects of the invention have been achieved in that a discharge lamp having a leakproof mercury-vapor control assembly has been provided which assembly will retain an amalgam-forming material, even when the latter is in a fluid state.

While several embodiments have been illustrated and described in accordance with the patent statutes, it will be appreciated that various modifications in the construction of the lamp and the mercury-vapor control assemblies can be made without departing from the spirit and scope of the invention.

For example, the knives 41 and 42 and recess 46 in the roller 40 may be designed in such a manner that roller lifts the severed short segments 45 of indium from the underlying wire mesh strip 34a. Also, an additional set or sets of knives spaced predetermined distances peripherally from the first pair can be used, if the diameter of the roller 40 is increased proportionately to prevent shortening the pressed lengths 32a of indi- For example, under certain conditions it may be desirable to apply half of the required amount of indium to a strip of wire mesh in the manner shown in FIG. 5, and then combine two such laminations in another roll-pressing operation to obtain a composite indiumimpregnated mesh ribbon having the proper indium loading.

Space limitations within the lamp may also require that the thickness of the collar assembly be increased by using a plurality of stacked indium-impregnated wire mesh strips. This type of assembly can very readily be made by merely repeating the indium-mesh pressing operation and using additional sets of rollers having properly spaced work faces.

I claim as my invention:

l. A mercuryfilled arc discharge device comprising;

an elongate sealed envelope having a fill of mercury,

means to energize said fill to arc-sustaining condition,

a foraminate container secured within the envelope, and

a solid body of mercury-amalgamative material enclosed in said container,

the foraminations of said container being of size to pass mercury vapor and to retain a substantial quantity of said amalgamative material in its fluid state during operation of the discharge device, and

said amalgamative material being effective to control mercury-vapor pressure during operation of the discharge device.

2. An electric discharge lamp comprising;

a sealed elongated envelope that contains spaced electrodes and an ionizable medium which includes mercury means to energize said electrodes and, in con unctlon with said ionizable medium, thereby initiate and sustain an arc discharge within said envelope, an assembly for controlling the mercury-vapor pressure during the operation of said lamp comprising a pair of spaced members supported within said envelope in overlying contacting relationship with a solid body of mercuryamalgamative material, at least one of said members being foraminous and said mercury-amalgamative material being accessible through the openings therein, and means associated with the peripheral portions of said members for retaining the mercury-amalgamative material between said members when said material is heated and in a fluid state. 3. The electric discharge lamp set forth in claim 2 wherein said amalgamative-material retaining means comprises a substance that is located at and extends along a peripheral edge of one of said members and repels said amalgamative material when the latter is in a fluid state.

4. The electric discharge lamp set forth in claim 2 wherein both of said members are foraminous.

5. The electric discharge lamp set forth in claim 2 wherein;

both of said members are foraminous,

the amalgamative material is spaced inwardly from the edges of both of said members, and

the peripheral edge portions of said members are disposed in contiguous overlapping relationship and define a border that is (a) devoid of amalgamative material and (b) extends completely around the periphery of said assembly and thus serves as the material-retaining means.

6. The electric discharge lamp set forth in claim 2 wherein;

said lamp comprises a fluorescent lamp,

said members comprise elongated pieces of wire mesh of substantially the same shape and dimensions,

said amalgamative material comprises a strip that has a width dimension less than that of said members,

said wire mesh members are disposed in facc-to-face aligned relationship, and

said strip of amalgamative material is centrally disposed and sandwiched between said wire mesh members so that the side edges of the resulting laminated structure are free of amalgamative material.

7. The fluorescent lamp set forth in claim 6 wherein;

said wire mesh members are fabricated from nickel and are of rectangular configuration,

said amalgamative material comprises a rectangular strip of indium that is of substantially the same length as the wire mesh members and thus extends to the end edges thereof, and

the indium-retaining means at the ends of said assembly comprises a layer of indium oxide and a layer of nickel oxide that cover the exposed portions of the indium strip and nickel wire mesh, respectively, and extend inwardly a predetermined distance from each end of the laminated assembly.

8. The fluorescent lamp set forth in claim 6 wherein;

said wire mesh members are of rectangular configuration,

said strip of amalgamative material is also of rectangular configuration but is shorter than said wire mesh members, and

said strip of amalgamative material is sandwiched and centrally located between said wire mesh members,

the relative dimensions of said strip of amalgamative material and wire mesh members being such that the edges of the wire mesh members extend at least one-sixteenth of an inch beyond the edges of the strip and thereby provide a border that is free of amalgamative material and extends completely around the periphery of the assembly. 

2. An electric discharge lamp comprising; a sealed elongated envelope that contains spaced electrodes and an ionizable medium which includes mercury, means to energize said electrodes and, in conjunction with said ionizable medium, thereby initiate and sustain an arc discharge within said envelope, an assembly for controlling the mercury-vapor pressure during the operation of said lamp comprising a pair of spaced members supported within said envelope in overlying contacting relationship with a solid body of mercury-amalgamative material, at least one of said members being foraminous and said mercury-amalgamative material being accessible through the openings therein, and means associated with the peripheral portions of said members for retaining the mercury-amalgamative material between said members when said material is heated and in a fluid state.
 3. The electric discharge lamp set forth in claim 2 wherein said amalgamative-material retaining means comprises a substance that is located at and extends along a peripheral edge of one of said members and repels said amalgamative material when the latter is in a fluid state.
 4. The electric discharge lamp set forth in claim 2 wherein both of said members are foraminous.
 5. The electric discharge lamp set forth in claim 2 wherein; both of said members are foraminous, the amalgamative material is spaced inwardly from the edges of both of said members, and the peripheral edge portions of said members are disposed in contiguous overlapping relationship and define a border that is (a) devoid of amalgamative material and (b) extends completely around the periphery of said assembly and thus serves as the material-retaining means.
 6. The electric discharge lamp set forth in claim 2 wherein; said lamp comprises a fluorescent lamp, said members comprise elongated pieces of wire mesh of substantially the same shape and dimensions, said amalgamative material comprises a strip that has a width dimension less than that of said members, said wire mesh members are disposed in face-to-face aligned relationship, and said strip of amalgamative material is centrally disposed and sandwiched between said wire mesh members so that the side edges of the resulting laminated structure are free of amalgamatIve material.
 7. The fluorescent lamp set forth in claim 6 wherein; said wire mesh members are fabricated from nickel and are of rectangular configuration, said amalgamative material comprises a rectangular strip of indium that is of substantially the same length as the wire mesh members and thus extends to the end edges thereof, and the indium-retaining means at the ends of said assembly comprises a layer of indium oxide and a layer of nickel oxide that cover the exposed portions of the indium strip and nickel wire mesh, respectively, and extend inwardly a predetermined distance from each end of the laminated assembly.
 8. The fluorescent lamp set forth in claim 6 wherein; said wire mesh members are of rectangular configuration, said strip of amalgamative material is also of rectangular configuration but is shorter than said wire mesh members, and said strip of amalgamative material is sandwiched and centrally located between said wire mesh members, the relative dimensions of said strip of amalgamative material and wire mesh members being such that the edges of the wire mesh members extend at least one-sixteenth of an inch beyond the edges of the strip and thereby provide a border that is free of amalgamative material and extends completely around the periphery of the assembly. 